An intrauterine device (IUD) is a small, often T-shaped device, containing copper or hormone (e.g., levonorgestrel), which is inserted into the uterus to provide long-acting, reversible contraception. As of 2007, IUDs are the most widely used form of reversible contraception, with more than 180 million users worldwide. IUDs typically are one of two types—copper or hormonal.
Copper IUDs primarily work by disrupting sperm motility and damaging sperm so that the sperm are prevented from joining with an egg. Copper acts as a spermicide within the uterus, increasing levels of copper ions, prostaglandins, and white blood cells within the uterine and tubal fluids. The increased copper ions in the cervical mucus inhibit the sperm's motility and viability, preventing sperm from traveling through a thickened cervical mucus and/or destroying it as it passes through. Copper IUDs have a typical first-year contraceptive success rate greater than 98 percent.
Most copper IUDs have a plastic T-shaped frame that is wound with pure electrolytic copper wire and/or has copper collars (sleeves). The arms of the frame hold the IUD in place near the top of the uterus. The Paragard® intrauterine copper contraceptive device (www.paragrad.com) and the generic TCU 380A are currently the most common copper IUDs. Copper IUDs can typically be implanted for up to 10 years.
The mechanism of action of a copper IUD is essentially a predictable electrochemical process of corrosion, driven by the IUD's immersion in the uterine fluid. Over time, the copper element (wires, beads, tubes, etc.) corrodes and releases copper ions. Typically, the release rate is governed by the surface area and volume of copper, the chemistry (especially pH) of the uterine fluid, and the specific composition and surface properties of the copper elements. The frame of the IUD on which the copper is attached is typically made of a flexible, non-corrosive polymer. Since typical polymers are not electrochemically active, they do not influence the ion release rate of the copper elements. Therefore, the copper ion release characteristics of a typical plastic-frame IUD are strictly governed by the amount, preparation and configuration of the copper itself. One challenge with copper IUDs has been that increased effectiveness typically means increased amounts of copper on the IUD, and increased amounts of copper typically lead to increased side effects, primarily increased menstrual and intermenstrual bleeding, and increased pelvic pain. Balancing effectiveness with minimization of side effects has been a continuing challenge for making copper IUDs.
One advantage of the copper IUD is its ability to provide emergency contraception up to five days after unprotected sex. It is generally known as the most effective form of emergency contraception available. Another advantage is that it contains no hormones, so it can be used while breast feeding, and fertility returns quickly after removal. Lastly, copper IUDs have been shown to be clinically effective for up to 10 years of continuous use. Disadvantages include the possibility of heavier menstrual periods and more painful menstrual cramping in some women.
A hormonal IUD, such as the Mirena® Levonorgestrel-releasing intrauterine system (www.mirena-us.com), uses the controlled release of a hormonal contraceptive such as Levonorgestrel (a progestin). The hormonal contraceptive released from a hormonal IUD prevents ovulation from occurring. The hormone also thickens the cervical mucus so that sperm cannot reach the fallopian tubes. Hormonal IUDs can typically be implanted for up to 5 years.
Hormonal IUDs do not increase bleeding as copper-containing IUDs do. Instead, they can often reduce menstrual bleeding or prevent menstruation altogether, and thus they are sometimes used as a treatment for menorrhagia (heavy menstrual bleeding). Hormonal IUDs have common side effects, however. The most common side effects with levonorgestrel IUDs are hormone-related effects, such as headaches, nausea, breast tenderness, depression and cyst formation.
Based on effectiveness and the types of side effects, copper IUDs are preferable for many women. Although currently available copper IUDs are very effective, it would still be advantageous to have improved copper IUDs. For example, it would be advantageous to have copper IUDs that were very effective but had minimal side effects.